Explained: How Covid-19 waves differ across the world and in India

While the US and UK are witnessing their fifth wave, India is seeing its third. But within the country, Delhi is in the midst of its fifth wave

The Centres for Disease Control and Prevention of the United States identifies three waves of the 1918 influenza pandemic. The first was in the spring of 1918, followed by an increase in infections in the fall and then a rise again in winter of 1919.

In 2009, some countries like the UK witnessed two waves of H1N1 influenza, whereas others like Thailand saw three. The Middle East Respiratory Syndrome (MERS) had three waves in Saudi Arabia until May 2015.

While India is battling the third wave of Covid-19, with incidence of infections rising, many countries worldwide are witnessing the fifth wave. South Africa, where Omicron was first identified, saw the fourth wave of infections owing to this new variant.

A wave is defined as an increase in infections in a particular geography, followed by a fall in infection numbers.

In the US, for instance, the first wave of Covid-19 started in March 2020, with a surge in cases. By April, daily infections had peaked at 90 cases per million people before they began to decline. Then, as a new variant of the virus replaced the original variant, cases began rising again in the US. They peaked at 200 cases per million per day before falling to 100 cases per million. The winter of 2020 saw another rise in infections in the country, with daily cases per million touching a high of 760 in January 2021, after falling to 34 daily cases per million in June 2021. The Delta variant caused the fourth wave in the US, when daily cases rose to 500 per million in September 2021. Omicron is responsible for the current surge in the US, with the country averaging 1,428 cases per million on January 3, 2022.

The UK witnessed a similar trajectory, with cases first rising in April 2020. Then there were two waves in quick succession as cases peaked in November 2020 before falling, and then peaking again in January 2021. In July, the country witnessed another surge, like the US, and has noticed a meteoric rise in cases since November.

While India has witnessed two waves so far and is facing the third one now, not all states have followed a similar trajectory. For instance, Delhi is witnessing its fifth wave currently. 

On the other hand, Kerala has witnessed three waves so far and Maharashtra two.