Few random FAQs on Covid-19 disease & Covid vaccines:
Q. Is it possible to get +ve RT-PCR test following COVID vaccination?
A. No.
Q. How long after the Covid vaccine do you get a +ve Antibody result?
A. Positive antibody in 40% by week 2, and over 90% by week 4.
Q. How long does immunity last after COVID19?
A. For those who recover from COVID19, immunity to the virus can last at least 8 months and maybe longer
Q. How long vaccine-induced immunity last?
A. We don’t know as yet. Most of the trials have 2-3 months follow up data only, we need a longer follow-up
Q. What a positive antibody test means?
A. Different serological tests measure diff types of Abs. Most commercial tests don’t measure neutralising Abs.
Q. If you have a positive antibody test means you’re immune to the virus?
A. For some infections, Abs might protect against reinfection. For others, they may not prevent reinfection, but symptoms may be milder. In yet other cases, Abs may provide no protection at all. Also, some test results may be “false positives.”
Q. If you test negative after >14 days of 2-doses of Covid vaccines, does it means you are not protected?
A. No, absence of Abs does not mean absence of protection. You may still have memory B cells & T cells responses that are not measured by routine lab tests.
Q. Is there any new study related to presence of Abs & risk of infection with COVID19?
A. A recent study published in @jamanetwok sows that Individuals who are seropositive for SARSCoV2 based on commercial assays may be at decreased future risk of SARSCoV2 infection.
Q. Do current COVID vaccine protect against asymptomatic infection?
A. Yes, they do but how best we don’t know for sure. Studies from Israel show that Pfizer vaccine provides a very high protection ~94% ag asymptomatic infection. But we need more data
Q. Can we differentiate Flu from COVID19 based on first symptoms?
A. According to a new study, while influenza typically begins with a cough, the first symptom of COVID19 is fever
Q. Can current generation of Covid vaccines effective against all new variants?
A. For UK B117 & Brazilian P1 variants, most vaccines are equally effective as with wild strain. Only marginal efficacy is lost. However, against SA B1351 variant, most vaccines are modestly efficacious.
Q. Is it true that current Covid vaccines are effective against serious disease even ag SA variant?
A. Yes. Since T cells prevent severe illness & death, & most of the T cells functions remain intact even ag these variants.
Q. Is it safe for me to get a COVID19 vaccine if I would like to get pregnant?
A. Yes. If you are trying to become pregnant now or want to get pregnant in the future, you may receive a COVID-19 vaccine when one is available to you.
Q. I definitely had COVID19, but my antibody test result is negative. Are false-negative results possible?
A. Yes, but they are not common: just 3.7% of people who had mild or moderate COVID19 had a negative Ab test afterwards.
Most often this arises because the COVID occurred several months prior to the Ab test.
Q. Is it true that those already infected & seropositive, need only a single dose of covid vaccine?
A. Yes, many studies have shown the utility of a single dose, & futility of more doses in seropositive individuals.
Q. Do we have any immunocorrelate of protection for prevention of SARSCoV2 infection?
A. No. However, in NHP studies, it’s seen that titers of NAbs ranging from 100-500 may provide sterilising immunity.
Q. Are the correlate of protection(CoP) against Covid disease and SARSCoV2 infection different?
A. Yes, in case of SARSCoV2 infection & vaccine studies, we measure NAbs as probable correlate. However, in Covid illness, the NAbs titers rise in regard with severity of disease. More severe disease ass with higher NAbs titers. Hence, NAbs are not protective.
Q. Then, what is the immune CoP against severe Covid?
A. It’s believed that IgG Abs against prefusion Spike proteins & IgG Abs against Fusion Peptide serve as a definite CoP against severe Covid & death. Presence of these Abs offer protection against severe disease and death.
(Compiled by Dr Vipin Vashishtha)
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