Fact Check: Is Omicron BA.5 the most infectious virus ever known?-thip

Quick Take

After the articles were published by media websites, several social media posts claimed Omicron BA.5 is highly transmissible as it has a basic reproduction number or R-naught (R0) of 18.6. We fact-checked and found the claim to be False.

The Claim

A media website named THECONVERSATION published an article titled ‘Australia is heading for its third Omicron wave. Here’s what to expect from BA.4 and BA.5’. Another media website named THEGUARDIAN published an article titled ‘New Covid subvariants BA.4 and BA.5 are the most contagious yet – and driving Australia’s third Omicron wave’.

Both the articles referred to similar studies to claim that the Omicron BA.5 variant is way more infectious than the original strain of coronavirus. Also, Omicron BA.5 variant is as infectious/or more than measles.

After these articles got published, a Twitter user wrote “The original Covid had an Ro value of 3.3, meaning each infected person infected 3.3 others. Low transmissibility, yet still killed millions. Measles is the highest with an Ro value of 18. The latest Covid subvariants have an Ro value of 18.6. If you think it’s over, guess again”.

Another Twitter user wrote “Letting BA5 rip will have an effect I don’t think many have factored in. It sounds like a nasty strain. If people realise it’s not #mild then for every wave afterwards there will be a shadow lockdown. Respirators can lower the viral load people are exposed to. Just sayin’”.

Fact Check

Does basic reproduction number or R-naught (R0) of 18.6 confirms Omicron BA.5 variant is highly transmissible?

Not exactly. A study describes basic reproduction number or R0 as the ‘number of secondary cases generated by a typical infectious individual when the rest of the population is susceptible (i.e., at the start of a novel outbreak)’.

To understand this definition better, we found another research paper that states that ‘the basic reproductive ratio or basic reproduction number (R0) is the average number of infected contacts per infected individual. At a population level, a value of R0 larger than one means that a virus will continue its propagation among susceptible hosts if no environmental changes or external influences intervene’. However, this is not the case with coronavirus variants.

The available evidence shows that there exist multiple factors which give one variant an advantage over others. These factors include changes in virus variants that make them transmissible inherently or the ability to avoid attack by the immune system in people who either got exposed to the virus or are vaccinated. Such advantages do not allow researchers to consider R0 as the sole measure of calculating transmissibility.

The outcome of our research is in similar lines to the social media posts shared by Natalie E. Dean, an American biostatistician specialising in infectious disease epidemiology, who wrote “Just because something has a 50% *growth advantage* in a population does not mean it is 50% more *transmissible.* Some (or most) of that growth advantage may come from immune evasion. 3/5” and “So if each new variant has a 50% growth advantage, it does not mean that R0 keeps increasing by 50%. And while new variants are more transmissible, R0 is not up to 18 (measles territory). The reality is that R0 is tricky to apply to our current situation. Interpret with care! 5/5”.

We also found a study that shows the basic reproduction number (R0) of measles is between 12–18. Besides published social media posts that spread misinformation, we could also find Tweets shared by social media users that debunk the claim as made.

THIP MEDIA TAKE: No evidence confirms Omicron BA.5 is the most infectious virus ever known. Also, the basic reproduction number or R-naught (R0) is not the sole factor that decides the transmissibility of a virus.

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