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Herd immunity can be achieved by letting the virus spread through the population

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Herd immunity is a key concept for epidemic control. It states that only a proportion of a population needs to be immune (through overcoming natural infection or through vaccination) to an infectious agent for it to stop generating large outbreaks.1 A key question in the current COVID-19 pandemic is how and when herd immunity can be achieved and at what cost. Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely.

Acquired immunity is established at the level of the individual, either through natural infection with a pathogen or through immunization with a vaccine. It refers to the indirect protection from infection conferred to susceptible individuals when a sufficiently large proportion of immune individuals exist in a population. This population-level effect is often considered in the context of vaccination programs, which aim to establish herd immunity so that those who cannot be vaccinated, including the very young and immunocompromised, are still protected against disease.

As a result, the whole community becomes protected — not just those who are immune. However, there are some significant problems with relying on community infection to create herd immunity to the virus that causes COVID-19.2First, it isn’t yet clear if infection with the COVID-19 virus makes a person immune to future infection. If it does not create immunity, herd immunity will not work.

Even if COVID-19 infection creates long-lasting immunity to coronavirus, a large number of people would have to become infected to reach the herd immunity threshold. Experts estimate that 70% of the population would have to recover from COVID-19 to halt the epidemic.3 On a separate related note, this amount of infection could also lead to serious, and potentially long-term, complications and millions of deaths. If many people become sick with COVID-19 at once, the healthcare system could quickly become overwhelmed.

It is therefore advisable to continue to use these practices to reduce the spread of COVID-19:

  • Wear a mask in public.
  • Keep your physical distance — 6 feet or about two arms’ lengths apart from other people.
  • Avoid in-person gatherings.
  • Wash your hands with soap and water.
  • Stay home if you do not feel well.
  • Get a test if you have COVID-19 symptoms.
  • Self-isolate if you have been around someone who is sick or tested positive.

Source

1 Fontanet A, Cauchemez S. COVID-19 herd immunity: where are we? Nat Rev Immunol. 2020;20(10):583-84. doi: 10.1038/s41577-020-00451-5.
2 Randolph HE, Barreiro LB. Herd Immunity: Understanding COVID-19. Immunity. 2020;52(5):737-41. doi: 10.1016/j.immuni.2020.04.012.
3 https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html

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Coronavirus

The virus is mutating so the current COVID vaccines won’t work

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A few days ago, Health Patrol carried out the update on the UK variant of the Coronavirus.1 According to the Ministry of Health & Family Welfare2, India, a new variant of SARS- CoV 2 virus [Variant Under Investigation (VUI)-20212/01] has been reported by the Government of United Kingdom (UK) to the World Health Organization (WHO). This variant is estimated by European Center for Disease Control (ECDC) to be more transmissible and affecting younger population and is defined by a set of 17 changes or mutations. Till date, there are 109 confirmed cases of the virus and scientists want to understand why these variants seem to be spreading so quickly. Adding to the sense of urgency is the worry that the variants could weaken immune responses triggered by vaccines and previous infection. This has also led to the question if this diminishes the potency of vaccines or overcomes natural immunity and lead to a spate of reinfections.3

The good news is that an 08th January update4 suggests the Pfizer–BioNtech vaccine is effective against a mutated form of the SARS-CoV-2 virus. Biotech firm Moderna in Cambridge, Massachusetts, which has developed an RNA-based vaccine, has said that it expects their vaccine to work against the UK variant and that tests are under way. Likewise, eminent evolutionary biologist Dr. Jesse Bloom3 from the Fred Hutchinson Cancer Research Center in Seattle, and other scientists are hopeful that the mutations in the variants will not substantially weaken the performance of vaccines. The vaccine shots produce a large number of neutralizing antibodies, so a small variation in the mutation should not affect the potency of the vaccine, they believe.

Source

1 https://healthpatrol.in/2021/01/08/the-uk-virus-cannot-infect-indians/
2 December 2020. https://www.mohfw.gov.in/pdf/SOPforSurveillanceandresponseforthenewSARSCov2variant.pdf
3 Ewwin Callaway. Nature2021;589:177-78.
4 Greaney AJ et al. 2021;Preprint at bioRxiv https://doi.org/10.1101/2020.12.31.425021

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Coronavirus

Vaccines won’t work on the new strain of Coronavirus found in the UK

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The first known case of the new variant B117, was recorded on 20 September and sequenced in early October. Further analysis and a December report said that the rate of transmission of the variant, known as B.1.1.7 or VUI 202012/01 (variant under investigation, year 2020, month 12, variant 01), was 71% higher than for other variants, and that it may also have a higher viral load.

There is currently no evidence that this strain causes more severe illness, although it is being detected in a wide geography, especially where there are increased cases being detected.

The new variant has mutations to the spike protein that the three leading vaccines are targeting. However, vaccines produce antibodies against many regions in the spike protein, so it’s unlikely that a single change would make the vaccine less effective.

The message from experts speaking at a Science Media Centre briefing on covid-19 was also coherent with this line of thought in that the new variant was unlikely to make vaccines ineffective. Peter Openshaw, Past-President of the British Society for Immunology and Professor of Experimental Medicine at Imperial College London, who sits on NERVTAG, said, “We know that natural infection or vaccination will produce quite an array of antibody responses. Although it’s predicted that some of the mutations that are present in the new variant will affect some of the sites that are recognised by the antibodies, it does not seem likely that it will affect all of them.

“It’s clearly important that all of this is tested, and people are working away in the laboratories as we speak to try to get some preliminary answers within the next few days, but it’s not quick science. We have to wait until they can grow the virus and test different serums. So this information could come out in the next few weeks.”

Therefore, as of now, the vaccine would be effective for the new variant as well.

Over time, as more mutations occur, the vaccine may need to be altered. This happens with seasonal flu, which mutates every year, and the vaccine is adjusted accordingly. The SARS-CoV-2 virus doesn’t mutate as quickly as the flu virus, and the vaccines that have so far proved effective in trials are types that can easily be tweaked if necessary.

Sharon Peacock, director of Covid-19 Genomics UK (COG-UK) consortium said (as reported in the BMJ, Dec. 16, 2020), “With this variant there is no evidence that it will evade the vaccination or a human immune response. But if there is an instance of vaccine failure or reinfection then that case should be treated as high priority for genetic sequencing.”

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The COVID-19 vaccine will make me immune to COVID-19

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The response to this question is still under discussion as evidence from new studies, interim results from phase III vaccine trials, and previous data from phase I and phase II trials support the notion that memory T cell responses to the vaccines, along with B cell antibody responses—in simpler terms, B-cells produce antibodies and similarly, T-cells are the central players in the immune response to a viral infection. These together, should provide good and possibly enduring immunity to SARS-Cov-2. With continuing public health measures, they should help lay a pathway out of the pandemic. High vaccine uptake will be critical to achieving individual and population immunity.1 

However, according to the WHO2, “It’s too early to know if COVID-19 vaccines will provide long-term protection. Additional research is needed to answer this question. However, it’s encouraging that available data suggest that most people who recover from COVID-19 develop an immune response that provides at least some period of protection against reinfection – although we’re still learning how strong this protection is, and how long it lasts. Most COVID-19 vaccines being tested or reviewed now are using two dose regimens.”

Therefore, for now, we can’t be certain if the COVID-19 vaccine will be effective enough to completely protect one from COVID-19. That is why we must not rely on a future vaccine to fight this pandemic – we must use all the tools we already have at our disposal, such as use of masks, physical distancing, hand hygiene, respiratory etiquettes, avoiding crowds, testing, contact tracing, quarantine/isolation.

Source:

1 Covid-19 vaccines: delivering protective immunity. BMJ 2020;371:m4838. doi: https://doi.org/10.1136/bmj.m4838
2 https://www.who.int/news-room/q-a-detail/coronavirus-disease-(covid-19)-vaccines?

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The new UK strain of Coronavirus is more dangerous!

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In the last few weeks, there has been a steady rise in the number of COVID infections in the south and east England. Samples from infected people have exposed the new virus. Already 1108 people have been infected with the new strain. The new variant of the Coronavirus found in the UK has been named VUI-202012/01 (the first “Variant Under Investigation” in December 2020) and is defined by a set of 23 mutations, including one on the receptor binding protein on the spike protein used by the virus to enter the human cells..

In common terminology, this virus is being referred to as the B117 and epidemiologists and virologists have found that B117 is 70% more transmissible than the other strains raising concerns of super-spreading events. One of its most significant mutation is an N501Y mutation in the spike protein that the virus uses to bind to the human ACE2 receptor. Changes in this part of spike protein may, in theory, result in the virus becoming more infectious and spreading more easily between people. This basically means that the spikes of the coronavirus with which they attach themselves to the healthy cells have mutated. This helps the coronavirus infect cells at a faster rate. The reproduction rate of this UK strain is also higher than other strains (reproduction rate refers to the number of people who can be infected from one infected person). 

Is it more dangerous then? We still don’t know that and are awaiting research and results to collate data on this particular aspect. Mutations that make viruses more infectious don’t necessarily make them more dangerous. The WHO has stated that “While initial assessment suggests that 202012/01 and 501Y.V2 do not cause changes in clinical presentation or severity, if they result in a higher case incidence, this would lead to an increase in COVID-19 hospitalizations and deaths.” 501Y.V2 is the new variant detected in South Africa.

A number of variants have already been detected in the UK. For example, the D614G variant is believed to have increased the ability of the virus to be transmitted and is now the most common type circulating in the UK, although it doesn’t seem to result in more severe disease.

Adapted from

1 Covid-19: New coronavirus variant is identified in UK. BMJ 2020;371:m4857. doi: https://doi.org/10.1136/bmj.m4857 (Published 16 December 2020)
2 Covid-19: What have we learnt about the new variant in the UK? BMJ 2020;371:m4944. doi: https://doi.org/10.1136/bmj.m4944
3 SARS-CoV-2 variants. Disease Outbreak News. 31 December 2020. https://www.who.int/csr/don/31-december-2020-sars-cov2-variants/en/

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Pregnancy is safe during the Covid-19 Pandemic

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A 2021 January publication1 discusses pregnancy during the Covid-19 Pandemic in greater detail. There are many unknowns for pregnant women during the pandemic. Clinical experience of pregnancies complicated with infection by other coronaviruses e.g., Severe Acute Respiratory Syndrome and Middle Eastern Respiratory Syndrome, has led to pregnant woman being considered potentially vulnerable to severe COVID-19 infection. Physiological changes during pregnancy have a significant impact on the immune system, respiratory system, cardiovascular function, and coagulation.2 These may have positive or negative effects on COVID-19 disease progression.3 The impact of SARS-CoV-2 in pregnancy remains to be determined, and a concerted, global effort is required to determine the effects on implantation, fetal growth and development, labor, and neonatal health. Asymptomatic infection presents a further challenge regarding service provision, prevention, and management.

From the current evidence base, it is difficult to draw absolute conclusions on whether pregnant women are at increased risk of severe consequences of COVID-19. Most women will experience mild or asymptomatic disease with no lasting consequences4; however, some centers have seen increased rates of ICU admission, and the need for mechanical ventilation in pregnant women. The lack of detailed data makes identification of risk factors, and the definitive comparison of pregnant and nonpregnant cohorts impossible. The lack of universal COVID-19 testing means that it is likely that the majority of cases go undetected. Vertical transmission is probable, but it appears rare, and in the majority of neonates, it has minimal impact. However, once more, this is impossible to fully assess until neonatal testing is routine. There are a number of unknowns, in particular, whether COVID-19 is an independent risk factor for preterm birth, whether infection during pregnancy is likely to lead to long-term adverse effects in offspring, and whether this effect is dependent on gestational age at infection. 

The review published in the journal Physiology Reviews1, further summarizes the research findings:

  1. The risk factors for severe COVID-19 are similar in pregnancy to the general population.
  2. Vertical transmission is plausible, but mechanisms are uncertain. Severe neonatal disease appears to be rare.
  3. Antenatal corticosteroid use for threatened preterm birth is likely to be safe for the mother, and corticosteroid use for severe maternal disease may be beneficial.
  4. Mothers with COVID-19 should be encouraged to breastfeed if they are able but should wear personal protective equipment to do so.
  5. Asymptomatic COVID-19 in pregnancy appears to be common but is of uncertain clinical significance.

Source:

1 Wastnedge EAN, Reynolds RM, van Boeckel SR, et al. Pregnancy and COVID-19. Physiol Rev. 2021; 101(1): 303–18.

2 Abdoli A, Falahi S, Kenarkoohi A, et al. The COVID-19 pandemic, psychological stress during pregnancy, and risk of neurodevelopmental disorders in offspring: a neglected consequence. J PsychosomObstetGynaecol 2020;41:247–48.doi:10.1080/0167482X.2020.1761321.

3 Baud D, Greub G, Favre G, et al. Second-trimester miscarriage in a pregnant woman with SARS-CoV-2 infection. JAMA 2020;323:2198–2200. doi:10.1001/jama.2020.7233.

4 Breslin N, Baptiste C, Gyamfi-Bannerman C, et al. Coronavirus disease 2019 infection among asymptomatic and symptomatic pregnant women: two weeks of confirmed presentations to an affiliated pair of New York City hospitals. Am J ObstetGynecolMFM 2 2020:100118. doi:10.1016/j.ajogmf.2020.100118. 

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